As the size of integrated circuits (ICs) continually decreases, chip manufacture is limited largely by critical dimension (CD). As used herein, “CD” means and includes the dimension of a smallest geometrical feature(s) (width of interconnect line, contacts, trenches, etc.) formed during semiconductor device manufacturing. Adjusting the CD and providing proper patterning of underlying material layers is difficult when using a photoresist material. However, photoresist integrity must be maintained throughout the photolithography process because any flaw or defect present on a patterned photoresist layer is transferred to an underlying layer(s) during a subsequent etch process.
One example of a photoresist defect that results in poor pattern transfer to the underlying layer is photoresist scum or scumming. Photoresist scum is caused by incomplete removal of portions of the photoresist layer, as well as formation of organic residues on portions of the underlying layer. Because the photoresist scum produces a variation in CD, the photoresist scum is typically removed prior to subsequent processing steps. The photoresist defect is removed in a so-called “descumming” process by plasma treating a patterned and developed photoresist layer with a source gas that includes at least 90% by volume oxygen (O2), with the balance being a so-called “forming gas” (such as 4% hydrogen (H2) in nitrogen (N2)). However, removing the photoresist scum with this source gas damages or deteriorates the photoresist layer, leading to line-edge roughness (LER) in layers patterned using the photoresist layer. As used herein, “LER” means and includes a deviation of a feature edge, as viewed from a top-down perspective, from a smooth, ideal shape. The deviation in LER results in increased CDs. As CD shrinks, LER becomes an increasingly large fraction of the CD tolerance budget.
FIGS. 1A-1D illustrate a portion of a conventional process employed in the fabrication of an intermediate semiconductor device structure 10 that includes a substrate 12, an oxide layer 14 and a photoresist layer 16. The photoresist layer 16 is patterned and developed. The pattern in the photoresist layer 16 has a width of “w1,” which, ideally, corresponds to the CD of the feature(s) ultimately to be formed in the oxide layer 14 or substrate 12. However, after development, photoresist defect 18 is present on portions of the intermediate semiconductor device structure 10, which affects w1 and prevents uniform and efficient etching of the underlying layers. When the above-mentioned source gas is used to remove the photoresist defect 18, remaining portions of the photoresist layer 16 may be damaged at an interface 20, which damage is schematically illustrated in FIG. 1B using a wavy line. When the pattern in the photoresist layer 16 is transferred to the underlying layers, the damage in the photoresist layer 16 produces a high degree of LER in the underlying layers. FIGS. 1C and 1D illustrate the intermediate semiconductor device structure 10 after etching the oxide layer 14 and removing the photoresist layer 16. The oxide layer 14 has a high degree of LER caused by the damage in the photoresist layer 16, which is schematically illustrated in FIGS. 1C and 1D using a wavy line. The feature formed in the oxide layer 14 has a width of w2 that deviates from w1 (w2 is either less than or greater than w1) due to the LER. The LER in the oxide layer 14 causes fluctuations in w2, which is problematic in maintaining overall CD during semiconductor device fabrication. As a result of the LER in the oxide layer 14, the CD of the feature to be formed in the oxide layer 14 undesirably varies from w1.
U.S. Pat. No. 5,980,768 discloses a method for removing photoresist mask defects from a wafer or for removing an organic antireflective layer. The method uses an etchant source gas that includes nitrogen and is substantially oxidant free to remove scumming layer defects and/or sloped foot photoresist mask defects. The etch is performed in a chamber, such as a chamber for dry etching, plasma etching, reactive ion etching, magnetically enhanced reactive ion etching, or electron cyclotron resonance.
Due to decreasing CDs, removing undesired portions of a photoresist mask becomes increasingly difficult without affecting LER. Thus, improved methods of removing photoresist defects are desirable.